iwlwifi: remove fw_monitor module parameter

This module parameter is no longer useful now that other debug
infrastructure was added to iwlwifi.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200418110539.03bd49c3432b.Ie62047d3b364b19c8c3584ea37790220466f2a8d@changeid